This invention relates generally to hoists for positioning loads during structural fabrication, and in particular, to a hydraulic auxiliary hoist and crane control for high precision load positioning.
Since the advent of hydraulic jacks or lifting cylinders, construction engineers have had the capability to raise and relocate structures, bridges or buildings of almost any size and tonnage—even entire city centers to allow new underground installations such as subways or essential repair work.
Weight is not typically a limiting factor in such positioning operations. A greater weight simply requires more cylinders. However, the extent of a straight lift is limited by the plunger stroke length of the cylinders used. Lifting a greater amount than the limiting stroke length typically requires the use of additional holding arrangements to permit the replacement or repositioning of cylinders for the next stage in the lifting operation.
Using a single crane, a heavy load, such as a large construction segment (roof section, floor section, wall section, large scale architectural ornamentation, bridge section, etc.), can be moved a long vertical distance with relative high speed. However, when precise geometric positioning of the load is required in a vertical and horizontal plane, multiple cranes and elaborate lift rigs are often required. Synchronizing the movements of multiple cranes in this fashion has proved to be difficult and risky. This synchronization difficulty limits the accuracy of the lifting operation and may lead to damage to the load, support fixtures, and/or cranes. Increased risk to the operators and workers is also present in such complicated positioning maneuvers.
Sudden crane starts and stops create oscillations during the critical stages of the lifting process. Weather conditions also provide a source of disturbances during heavy load positioning applications, as wind can blow a lifted section and thereby induce dangerous side loads on the crane, for which the crane was not designed to bear.
One system for positioning a load includes a plurality of hydraulic cylinders attached by cables to a crane or other lift mechanism. The hydraulic cylinders are manually controlled to adjust the position of the load. Such manual systems require multiple jogging operations that can induce oscillations. Moreover, the position of only one cylinder is typically changed at a time. This situation can cause the load to become unbalanced.
Therefore, a need exists for high precision load positioning system that may be implemented without the synchronization and loading issues associated with multiple crane operations or manually controlled lifting cylinders.